Rectum and Anal Canal

Question 1

Is the rectum retro, intra, or secondary retroperitoneal ?

Answer 1

Partially retroperitoneal

− Has mesorectum, NOT mesentery

Question 2

Describe the anatomical path of the rectum.

Answer 2

1) Begins in front of the 3rd sacral vertebra
2) Follows the curve of the sacrum and coccyx
3) Ends in front of the tip of the coccyx by piercing the pelvic diaphragm and becoming continuous with the anal canal

Question 3

Describe the main structural components of the rectum.

Answer 3

• Has lateral curvatures, coinciding with rectal folds or valves internally
• The lower part of the rectum is expanded to form the rectal ampulla
• Pararectal fossa on both sides
• Lacks taenia, haustra or epiploic appendices
• Inside there are 3 transverse mucosal folds which do not disappear when rectum is distended

Question 4

What is the main function of the rectum ?

Answer 4

Storage of faeces prior to defecation

Question 5

At which levels are the mucosal folds of the rectum found ?

Answer 5

5-6 cm from anus
8-9 cm from anus
11-13 cm from anus

Question 6

What is the junction between anus and rectum called ? How is it formed ?

Answer 6

Perineal flexure (anorectal junction or angle)

Caused by anterior pull of the rectum by puborectal muscle

Question 7

State the main anatomical relations of the rectum in the male.

Answer 7

• Bladder (anteriorly)
• Prostate (palpable per rectum) (anteriorly)
• Rectovesical pouch (anteriorly, between rectum and bladder)
• Rectoprostatic fascia (Denonvillier’s fascia) (anteriorly, between rectum and prostate)
• Pelvic plexus (at risk in rectal surgery) (laterally)
• Seminal vesicles (anterolaterally)
• Ductus deferens (anterolaterally)
• Ureter (anterolaterally)

Question 8

State the main anatomical relations of the rectum in the female.

Answer 8

• Bladder (anteriorly)
• Uterus (anteriorly)
• Rectouterine pouch (of Douglas) (anteriorly, between rectum and uterus)
• Rectovaginal fascia (anteriorly, between rectum and vagina)
• Pelvic plexus (at risk in rectal surgery) (laterally)
• Ureter (anterolaterally)

Question 9

How far are rectouterine, and rectovesical pouches from the anorectal angle respectively ?

Answer 9

Rectouterine pouch (of Douglas): 5.5 cm above anorectal angle
Rectovesical pouch: 7.5 above anorectal angle

Question 10

How long is the anal canal ?

Answer 10

Approximately 4cm long

Question 11

Where does the anal canal start, and finish ?

Answer 11

From the pelvic diaphragm to the anus

Question 12

State the main anatomical relations of the anal canal.

Answer 12

Related to ischioanal fossa laterally

Question 13

Identify the main muscles surrounding the anal canal.

Answer 13

• Surrounded by levator ani, external anal sphincter and internal anal sphincter
• The anorectal ring is a muscular structure at the junction of the anal canal and the rectum.

Question 14

Identify the main components of the anorectal ring.

Answer 14

It includes the puborectalis sling and upper portions of the internal and external sphincters.

Question 15

What are possible clinical consequences of abnormalities of the anorectal ring ?

Answer 15

Division of the anorectal ring results in incontinence.

Question 16

What kind of muscle makes up the internal anal sphincter ? Where does this sphincter end ?

Answer 16

− Smooth muscle, autonomic
− Derived from circular muscle layer
− Ends at intersphincteric groove

Question 17

What kind of muscle makes up the external anal sphincter ? Where does this sphincter end ?

Answer 17

− Striated muscle
− One functional unit with deep, superficial and subcutaneous parts
− Fuses with puborectalis

Question 18

Describe the main structural components of the anal canal.

Answer 18

♣ Below anorectal line, in the upper part of the anal canal, there are 8-10 longitudinal folds called anal columns (formed primarily by branches of the superior rectal vein, but also superior rectal artery, lymphatics, and nerves) (in the hemorrhoidal zone)
-Some of the columns are bigger than the others. These are called anal cushions, usually at 3, 7, 11 o’clock in the lithotomy position. These cushions help sphincters close the lumen.

♣ Anal columns unite with each other inferiorly and form anal valves

♣ Superior to each valve is a depression termed an anal sinus (crypt), which contain mucous glands

♣ The anal valves together form a circle in the anal canal called pectinate (dentate) line (where the anal membrane was in the fetus)

• Superior to the pectinate line is the hemorrhoidal zone (area of anal columns)
• Inferior to the pectinate line is a transition zone known as the anal pecten

♣ Anal pecten ends inferiorly at the anocutaneous line (“white line”), or where the lining of the anal canal becomes true skin (below that line is the cutaneous zone)

For a diagramatic representation of this, refer to slide 18 in lecture.

Question 19

What is the function of the mucous glands present in the crypts superior to the anal valves ?

Answer 19

Lubricate the feces

Question 20

Describe the nerve supply of the anal pecten.

Answer 20

Supplied by inferior rectal nerve

Sensitive to pain, temperature, touch, pressure

Question 21

Describe the arterial supply of the rectum and anal canal.

Answer 21

SUPERIOR 1/3: inferior mesenteric artery
→ Superior rectal artery

MIDDLE 1/3: internal iliac
→ Middle rectal artery (variable, sometimes absent)

BELOW ANORECTAL LINE: Internal pudendal
→Inferior rectal artery

May be contribution form median sacral

Question 22

What is the clinical significance of the median sacral artery possibly contributing to the arterial supply of the anal canal and rectum ?

Answer 22

A contribution from the median sacral may cause bleeding during surgery

Question 23

Describe the veinous drainage of the rectum and anal canal.

Answer 23

1) Internal (submucosal) Rectal Plexus:
− Drains to superior rectal vein

2) External Rectal Plexus:
a. Superior 1/3: Superior rectalinferior mesenteric →
Hepatic portal vein
b. Middle 1/3: Middle rectal → internal iliac + internal pudendal veins
c. Inferior 1/3: Inferior rectal → internal iliac + internal pudendal veins

Question 24

Where are the internal, and external rectal plexuses found respectively ?

Answer 24

Internal rectal plexus
− In submucosa

External venous plexus
− Between and outside muscle layer (i.e. between and outside sphincters)

Question 25

Describe the lymphatic drainage of the rectum and anal canal.

Answer 25

General path is: Epicolic (along the wall) → paracolic (along the vessels) →intermediate (ın mesorectum) → principal lymph nodes.

The principal lymph nodes for:

1) Superior rectum→ Inferior mesenteric nodes
2) Inferior rectum and proximal anal canal →Internal iliac nodes
3) Distal anal canal → Superficial inguinal nodes

Question 26

Describe the nerve supply of the rectum and anal canal.

Answer 26

PARASYMPATHETIC from S2-4 via pelvic splanchnic nerves →pelvic (inferior hypogastric) plexus
− Increases peristaltism
− Relax anal sphincter
− Visceral senses

SYMPATHETICS from L1-2(3) via lumbar splanchnic nerves
− Contract anal sphincter

SOMATIC nerves from S2-4→ pudendal nerve
− Supplies external anal sphincter, adjacent pelvic floor muscles (puborectalis)

SOMATIC afferent below the pectinate line of the anal canal is pudendal nerve

Question 27

Identify possible causes of hemorrhoids.

Answer 27

Due to blockage of drainage of hemorrhoidal plexus (AKA internal and external rectal plexuses), possibly due to:

1. Portal hyperT
2. Tumors
3. Pregnancy
4. Chronic constipations (perhaps due to low fiber diet)
5. Sedentary life

Question 28

What are the main kind of hemorrhoids ?

Answer 28

Internal haemorrhoids- internal plexus involved

External haemorrhoids- external plexus involved

Question 29

Describe how fecal continence occurs, naming all the structures responsible for this.

Answer 29

• Levator ani and puborectalis, making rectoanal angle more acute; internal and external anal sphincters; abdominal pressure flattens anterior wall of lower rectum over upper anal canal; anal cushions close the canal
• The rectum can partially fill without an increase in pressure (c.f. bladder); the anal canal sensation (specialised receptors) can allow the cortex to distinguish between gas, fluid and solid faeces; there are stretch receptors in levator ani and the tissue around the anal canal
• Eventually, rectal pressure forces its contents into the anal canal, but defecation is prevented by learned cortical inhibition; only gas may be allowed to escape; the external anal sphincter forces faeces back up in to the rectum

Question 30

Describe the nervous processes involved in defecation.

Answer 30

When defecation is allowed:
♠ Cortical inhibition is released, via the corticospinal tracts (like micturition)
♠ Abdominal pressure is increased
♠ Puborectalis relaxes allowing the rectoanal angle to straighten; the external sphincter anal splinter relaxes (somatic S2, S3, S4)
♠ The lower colon and rectum contract while the internal anal sphincter relaxes (parasympathetic pelvic splanchnics S2, S3, S4 via pelvic plexus)
♠ The reflexes are therefore at S2, S3, S4
♠ Incontinence: Loss of control following cortical or cord lesions above S2, S3, S4; or damage to the external anal sphincter during obstetric or perineal procedures; or entrapment of the pudendal nerve